This invention relates generally to electric motors and more particularly to a rotor assembly and method of making the same.
In many applications employing electric motors, particularly electronically commutated motors, it is desirable to periodically change the direction of rotation of a rotor assembly in the motor to oscillate a driven apparatus. Such applications include, for example, washing machines wherein such oscillating electric motors are used to drive an agitator. When such oscillating electric motors are used, they negate the need for complex and expensive transmissions otherwise required to convert a rotating motion into an oscillating motion.
A problem encountered in the use of oscillating electric motors is that of the oscillatory torque establishing a fatigue load in the rotor assembly. This fatigue load is established at an interface between a flux ring and a magnetic body disposed thereon. Inertial effects associated with this fatigue load cause the development of a cyclic shear stress field, i.e. a shear stress field which reverses direction in each cycle of rotor oscillation, in a direction circumferential to the flux ring. This cyclic shear stress field eventually causes loosening and dislodgement of the magnetic bodies from the flux ring.
It would thus be desirable to provide a rotor assembly which is not subject to the ill effects caused by the cyclic shear stress field. It would be further desirable if such a rotor assembly could be economically fabricated using conventional technologies.